3.6. Additional Information on XML Schema

Although XML schemas have been standardized, the area of validation is still a research subject and alternatives have been proposed: see [29] for a comparison between some of them. Interesting links are being made with relational database models [34] in order to build on its strong theoretical background. Schemas and the validation process are being formalized [13].

We have only skimmed over the subject of validation of XML files but the same essential ideas apply throughout. On top of the official and informal information available at http://www.w3.org/xml/Schema, some good sources of information and interesting tutorials can be found in the following resources:

http://www.XML.com
is maintained by the O'Reilly editor with many excerpts from their books.
http://www.XML.org
is a market-oriented site with interesting files in the resources section.
http://www.mulberrytech.com/quickref/XMLquickref.pdf
a very useful XML Syntax Quick Reference Sheet (US letter size).
http://www.xfront.com/xml-schema.html
a complete XML Schema tutorial in roughly 150 Microsoft Powerpoint slides with example source code
http://www.xfront.com/schematron/
Tutorial and links for Schematron
http://www.xmlspy.com
XMLSpy is a commercial XML editor on the Microsoft Windows platform, with a powerful structure editor and internal validation and real-type suggestions of allowable elements attributes (strangely, these suggestions are not adequate in the text view i.e. the mode in which XML tags are explicitely typed). It is easy to switch between the text view and the structural view of the editor. There is also a good stylesheet designer module (Stylevision) to create stylesheet transformations interactively and graphically. These transformations can then be used as a basis for what is called the authentic view which can effectively hide the XML tags from the user of an XML document.
http://www.oxygenxml.com/
<oXygen/> is an XML editor for Microsoft Windows, Linux, MacOS X and Solaris. Real-time valid suggestions are offered in the text view. Validation can be done within the editor. Stylesheets transformations can be displayed in a window of the editor. It also features table and tree editing modes and a similar graphical output of a schema to what is provided by XMLSpy. Unfortunately, it is not possible to edit the schema graphically. It is one of the few XML editors that also offers real-time Schematron validation. For XML files, there is also an author mode which allows a tagless XML editing of the file directly from the rendered version through Cascading Style Sheets. As the formatting allowed with CSS is less powerful than what is possible with StyleSheets, this mode does not allow a full rendering like the authentic mode of XMLSpy but it has the advantages of being based on open standards. But for documented oriented XML files such as the ones written in DocBook or XHTML, this mode is quite convenient and user friendly.
http://www.thaiopensource.com/nxml-mode/
nXML mode in Emacs [19] offers real-time valid suggestions for editing XML files in text mode only when their schema is written in RELAX NG. Trang can be used for translating an XML Schema or a DTD into RELAX NG.